1. Field of the Invention
The present invention relates to a pneumatic tire.
More specifically, the present invention relates to a pneumatic tire which uses, as an inner liner layer, a laminated sheet obtained by laminating an air permeation preventing layer, made of any one of a thermoplastic resin and a thermoplastic elastomer composition containing a blend of the thermoplastic resin and an elastomer, and a tie rubber layer, and which has high durability making it possible to prevent development of a crack in the tie rubber layer that occurs around a splice portion of the laminated sheet after the tire starts to be used.
2. Background Information
In recent years, pneumatic tires have been proposed and studied which use, as an inner liner layer, a laminated sheet including an air permeation preventing layer, made of a thermoplastic resin or a thermoplastic elastomer composition containing a blend of the thermoplastic resin and an elastomer, and a tie rubber layer Japanese patent application Kokai publication No. 2009-241855.
In general, to manufacture such a pneumatic tire, a manufacturing method is employed in which a laminated sheet including a sheet-shaped object for the air permeation preventing layer made of a thermoplastic resin or a thermoplastic elastomer composition obtained by blending the thermoplastic resin and an elastomer, and including a rubber (tie rubber) sheet to be cured and adhered to the thermoplastic resin or the thermoplastic elastomer composition obtained by blending the thermoplastic resin and the elastomer, is wound around a tire making drum and lap spliced and is then subjected to a tire cure-molding process.
A pneumatic tire may be manufactured by pulling out the laminated sheet, which has been wound into a rolled shape, by a predetermined length from the rolled shape and cutting the laminated sheet in the length, winding the laminated sheet around a tire making drum, lap splicing the laminated sheet on the drum, and further cure-molding the laminated sheet to form an inner liner layer. In this case, however, a crack may be developed around a splice portion after the tire starts to be used, thereby causing in some cases delamination between the sheet of the thermoplastic resin or the thermoplastic elastomer composition and the tie rubber cured and adhered to the sheet of the thermoplastic resin or the thermoplastic elastomer composition, which collectively constitute the inner liner layer.
To explain this with drawings, as shown in FIG. 4(a), a laminated sheet 1 including a sheet 2, made of a thermoplastic resin or a thermoplastic elastomer composition obtained by blending the thermoplastic resin and an elastomer, and a tie rubber layer 3 is cut to a desired size (length) with an edge tool or the like. Then, the laminated sheet 1 is lap spliced on a tire making drum (unillustrated) in such an annular shape that both end portions thereof form a lap splice portion S. Moreover, other parts (unillustrated) necessary for manufacturing the tire are wound and then cure-molding are performed with a bladder.
As a result of the cure-molding, an inner liner layer 10 is formed which includes the sheet 2, made of the thermoplastic resin or the thermoplastic elastomer composition obtained by blending the thermoplastic resin and the elastomer, and the tie rubber layer 3 as shown in the view in FIG. 4(b) as a model. Around the lap splice portion S, the sheet 2 made of the thermoplastic resin or the above-mentioned thermoplastic elastomer composition forms a portion which is exposed and a portion which is buried inside the tie rubber layer. This sheet 2 made of the thermoplastic resin or the above-mentioned thermoplastic elastomer composition constitutes an air permeation preventing layer 2a. In FIG. 4(b), the direction indicated by an arrow D is the tire circumferential direction.
The phenomenon in which the sheet 2 (air permeation preventing layer 2a) made of the above-mentioned thermoplastic resin or thermoplastic elastomer composition and the tie rubber layer 3 cured and adhered thereto are delaminated from each other after the tire starts to be used occurs particularly at a spot shown in FIG. 4(b) where the sheet 2 (air permeation preventing layer 2a) made of the thermoplastic resin or the thermoplastic elastomer composition is exposed and also in the vicinity 4 of the tip of the sheet 2 among others. In the beginning, a crack is developed between the sheet 2 (air permeation preventing layer 2a) made of the thermoplastic resin or the thermoplastic elastomer composition and the tie rubber layer 3, and the crack may further grow into the delamination phenomenon.
The reason for this phenomenon, specifically, the development of a crack between (on an interface of) the air permeation preventing layer 2a and the tie rubber layer 3 is considered to be attributable to the fact that the air permeation preventing layer 2a, formed of the sheet of the thermoplastic resin or the thermoplastic elastomer composition, usually has high rigidity. Accordingly, a portion of the tie rubber layer which is sandwiched vertically by ends of the air permeation preventing layer 2a is fixed and strain thereof is suppressed. On the other hand, strain cannot be suppressed at a portion of the tie rubber layer 3 in the vicinity 4 of the tip of the air permeation preventing layer 2a which is not sandwiched vertically by the ends of the air permeation preventing layer 2a and a large stress occurs as a consequence. Moreover, the crack, development is considered to be attributable to a situation where cure adhesion may not be sufficiently high between the sheet 2 of the thermoplastic resin or the thermoplastic elastomer composition and the tie rubber layer 3, and so on.
On the other hand, when the cure adhesion is sufficiently high between the sheet 2 of the thermoplastic resin or the thermoplastic elastomer composition and the tie rubber layer, strain by stress is concentrated on and around a spot inside the tie rubber layer 3 indicated by C in of FIG. 4(b), thereby frequently causing cracks. The strain by stress is concentrated on and around the above-mentioned spot indicated by C in FIG. 4(b) where the tie rubber layer 3 is exposed to the surface. For this reason, the strain by stress having the direction of strain in conformity to the tire circumferential direction is generated in the aforementioned spot in the tie rubber layer 3. This is considered as a cause of the development of a crack around the spot C in the tie rubber layer.